Centrifugal casting apparatus for forming a cast wall member extending transversely across an elongated bundle of substantially parallel hollow filaments of a fluid permeation separation apparatus



1970 J. GEARY, JR,, ETAL 3,492,698

CENTRIFUGAL CASTING APPARATUS FOR FORMING A CAST WALL MEMBER EXTENDING TRANSVERSELY ACROSS AN ELONGATED BUNDLE OF SUBSTANTIALLY PARALLEL HOLLOW FILAMENTS OF A FLUID PERMEATION SEPARATION APPARATUS Original Filed Dec. 22, 1965 6 Sheets-Sheet 1 m m \8: nN: 3: ".WHM H. lll mmmu h m W MMMM wmm E "D Qsk U a, a QQH m m H m m m m m m W 37i A M a W? iii! ww mmm Al SE 522: 5555.; +23. .mwaw

Feb. 3, 1970 J. E. GEARY, JR, ET AL 3,492,698

CENTRIFUGAL CASTING APPARATUS FOR FORMING A CAST WALL MEMBER EXTENDINGv TRANSVERSELY ACROSS AN ELONGATED BUNDLE OF SUBSTANTIALLY PARALLEL HOLLOW FILAMENTS OF A FLUID PERMEATION SEPARATION APPARATUS Original Filed Dec. 22, 1965 6 Sheets-Sheet 2 is: new Efifiwa M Q2 zfim N3 53% @1 an 3: w 2:53: 2: 35 1 $552522 mm 5% 32: m2 2 L225: :53 LQEEE @5253 /m w: :2 fan 35252: 3 5:23:52 aw flw 5:522 E2 5 2n :5; 25 522 355m 505% O5 Emit 25:52 SHEEP? 225: Emit Feb. 3, 1970 .1. E. GEARY, JR.. ETAL 3,492,698

CENTRIFUGAL CASTING APPARATUS FOR FORMING A CAST WALL MEMBER EXTENDING TRANSVERSELY ACROSS AN ELONGATED BUNDLE OF SUBSTANTIALLY PARALLEL HOLLOW FILAMEN'IS OF A FLUID PERMEATION SEPARATION APPARATUS Original Filed Dec. 22, 1965 v 6 She ets-Sheet 5 WM? i mmw" Feb. 3, 1970 J. E. GEARY, JR., ETAL 3,49

CENTRIFUGAL CASTING'APPARATUS FOR FORMING A CAST WALL MEMBER 1 EXTENDING TRANsvERsELY-Acrwss AN ELONGATED BUNDLE OF SUBSTANTIALLY PARALLEL HOLLOW FILAMENTS OF A FLUID PERMEATION SEPARATION APPARATUS Originalyl-iled Dec. 22, 1965 6 Sheets-Sheet 4 FIG. I I

Feb. 3, 1970 J. E. GEARY, JR. ET AL 3,492,698

CENTRIFUGAL CASTING APPARATUS FOR FORMING A CAST WALL MEMBER EXTENDING TRANSVERSELY ACROSS AN ELONGATED BUNDLE OF SUBSTANTIALLY PARALLEL HOLLOW FILAMENTS OF A FLUID PERMEATION SEPARATION APPARATUS Original Filed Dec. 22, 1965 6 Sheets-Sheet 5 INVENTORS HES EDWARWGEARY, JR. LLIAI EDIA'RI) HARSCH OHN MURDOCK MAXWELL RICHARD DONALD REG0 Feb; 3, 1970 J. E. GEARY, JR., ET AL 3,492,698

CENTRIFUGAL CASTING APPARATUS FOR FORMING A CAST WALL MEMBER EXTENDING TRANSVERSELY ACROSS AN ELONGATED BUNDLE OF SUBSTANTIALLY PARALLEL HOLLOW FILAMENTS OF A FLUID PERMEATION SEPARATION APPARATUS Original Filed Dec. 22, 1965 6 Sheets-Sheet 6 is 3% E EN no u 5 ix INVENTORS Y. JR.

H LL ATTORNEY CEO 7 mu N HARM D I. IN A mum! D I S M fiuMw Mflmm w United States Patent 3,492,698 CENTRIFUGAL CASTING APPARATUS FOR FORMING A CAST WALL MEMBER EX- TENDING TRANSVERSELY ACROSS AN ELONGATED BUNDLE OF SUBSTAN- TIALLY PARALLEL HOLLOW FILAMENTS OF A FLUID PERMEATION SEPARATION APPARATUS James Edward Geary, Jr., Claymont, Del., William Edward Harsch, Staunton, Va., John Murdock Maxwell, Glen Farms, Md., and Richard Donald Rego, Wilmington, Del., assignors to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware Original application Dec. 22, 1965, Ser. No. 515,535. Divided and this application Apr. 29, 1968, Ser. No. 739,981

Int. Cl. B29c /04 U.S. Cl. 1826 2 Claims ABSTRACT OF THE DISCLOSURE A centrifugal casting apparatus for forming in place an effective fluid-tight substantially precisely defined cast header wall member extending transversely across an elongated bundle of substantially parallel hollow filaments extending through an elongated hollow casing during the specialized manufacture of the specific type fluid permeation separation units described. The apparatus utilizes high centrifugal forces to control the uniformity of the cast wall structure, the uniformity of the surface of the wall structure, and the wall position relative to the bundle and casing.

CROSS REFERENCE TO RELATED APPLICATION AND PATENT This application is a division of application Ser. No. 515,535 filed Dec. 22, 1965, now Patent No. 3,339,341, issued Sept. 5, 1967 to Maxwell et al.

FIELD OF THE INVENTION This invention relates generally to the field of separating fluid by utilizing their different permeation rates through membrane elements in the form of small hollow filaments made of organic polymeric compositions. More specifically, the invention involves novel and improved apparatus arrangements for use in the production or fabrication of the new, improved, and specialized fluid separation apparatus described.

PRIOR ART BACKGROUND OF THE INVENTION Fluid separation apparatus and methods utilizing hollow filaments of polymeric compositions have been disclosed in the prior art. However, careful examination of such disclosures indicates that the apparatus and process arrangements represented experimental or ineflicient, impractical embodiments of the early ideas in the field. In addition, such prior art arrangements were of such desings and possessed features which would not lend themselves either to elfective commercial operation or to practical, reliable commercial manufacturing techniques.

It is one general object of this invention to provide new and improved fluid separation apparatus and processes for many fluid separations which overcome the deficiencies and disadvantages of the prior art arrangements especially with respect to efficient, flexible, and reliable commercial operation, and also with respect to simple, direct, and economical designs and practical commercial manufacturing techniques.

It is an additional general object of the invention to provide new and improved commercial manufacturing ice equipment for use in producing the novel, improved, and specialized fluid separation apparatus disclosed.

SUMMARY OF THE INVENTION Generally stated, according to the invention, certain Wall defects are prevented and eflective fluid-tight header wall members are produced in the specialized permeation separation units described by using the particular centrifugal casting apparatus of the invention wherein a rotatable mold assembly utilizes high centrifugal forces to cast in place and control the position and uniformity of the header wall member cooperating with an elongated bundle of hollow filaments extending through a hollow casing member of the units described. The casting apparatus is also provided with a supporting base on which the rotatable mold assembly is mounted, a drive means to rotate the assembly about an axis means mounted on the rotatable assembly for supporting the elongated bundle of hollow filaments and securing the bundle for rotation with the assembly in a position such that the axis is substantially perpendicular to the direction in which the filaments and bundle extend and such that the axis is spaced from the end portions of the bundle, the casting apparatus further provided with at least one mold unit carried by the rotatable assembly, the mold unit having a cavity constructed, arranged, and positioned to surround and contain one end portion of a bundle of hollow filaments secured on said assembly and to maintain a mass of solidifiable liquid in engagement with one end portion of such a bundle during rotation, said apparatus further provided with means carried by the rotatable assembly for introducing the solidifiable liquid into engagement with the end portion of the bundle in the mold cavity during rotation of the assembly, the drive means adapted to rotate the rotatable assembly, mold unit, bundle and liquid at sufl'lcient speeds such that the liquid is maintained in bubble-free, void-free condition in desired position during introduction, and solidification of the liquid and such that centrifugal forces prevent wicking of the liquid along the filaments of the bundle due to capillary action which wicking would destroy the desired precisely defined nature of the cast wall member surface.

The means and methods by which the objects of the invention are achieved, as well as additional objects and advantages thereof will be apparent from a consideration of the following specification and claims taken in conjunction with the accompanying drawings.

In the drawings:

FIGURE 1 is a partial longitudinal sectional view of the specialized fluid separation unit produced using the apparatus of this invention with parts broken away to show the details of its construction.

FIGURES 2 and 2a are partial transverse cross-sectional views taken at line 22 of FIGURE 1, FIGURE 211 being somewhat enlarged.

FIGURE 3 is a partial transverse cross-sectional view taken at line 33 of FIGURE 1.

FIGURE 4 is a partial greatly enlarged transverse crosssectional view of an indicated portion of a group of hollow filaments of the unit shown in FIGURE 2.

FIGURES 5a, 5b, 5c, and 5d are partial showings of illustrative porous sheath members used to surround and constrain the filaments in the groups and bundles.

FIGURE 6 is a schematic diagrammatic showing of a four stage permeation separation system or arrangement utilizing the specialized permeation separation units of the type shown in FIGURE 1.

FIGURE 7 is a general somewhat schematic perspective view of an apparatus arrangement for forming individual groups of small filaments in the form of hanks, bundles or loops of continuous hollow filaments.

FIGURE 8 is a simple side elevational view of a single hank or loop of continuous hollow filaments in elongated flattened configuration which forms a group or sub-bundle for eventual assembly in the permeation separator unit embodying principles of this invention.

FIGURE 9 is a simple side elevational view showing a single hank or loop of continuous hollow filaments in elongated flattened configuration being encased in and radially constrained by an elongated porous sheath member to make an encased group or bundle.

FIGURE 10 is a partial side elevational view showing a plurality of groups or sub-bundles of hollow filaments, each encased in its porous sheath member, being assem bled to form the larger bundle before positioning of the larger bundle in the casing of a permeation separator unit of the invention.

FIGURE 11 is a partial elevational view of a bundle of assembled groups of sheath encased hollow filaments in position for movement into the unit casing after the final porous sheath member or members is positioned around the assembled bundle.

FIGURE 12 is a view similar to FIGURE 11 showing a final porous sheath member being positioned on a bundle of assembled filament groups to radially constrain the same to dimensions which permit positioning of the assembled bundle in the unit casing.

FIGURE 13 is a partial longitudinal sectional view of a bundle of assembled filament groups in position in the unit casing with a mold assembly of the invention operatively mounted on the casing for formation of a cast end closure member for the unit casing.

FIGURE 14 is a view similar to FIGURE 13 showing the completed cast end closure member positioned in the unit casing With the mold assembly removed and before the unwanted excess portions of the cast end closure member is cut away.

FIGURE 15 is a view similar to FIGURE 14 of a completed modified cast end closure member positioned in unit casing as in FIGURE 14, the cast end closure member being the type formed against a radially outwardly positioned layer of heavy immiscible liquid in the mold assembly during centrifuging in order to maintain the ends of the bundle of filaments free of the cast material.

FIGURE 16 is a partial perspective view of a centrifuging aparatus embodying principles of the invention as used in forming the east end closure member for the permeator separator unit casing, showing a casing and cooperating mold assemblies in operative engagement with the centrifuging apparatus.

FIGURE 17 is a partial side elevational view of a modified version of the centrifuging apparatus shown in FIGURE 16 showing a plurality of unit casings in position for formation of one of their cast end closure members.

A basic unit of the specialized fluid separation apparatus made using the apparatus of the invention is shown in FIGURES 1, 2, 3, and 4 of the drawings. Generally speaking, this apparatus depends, for its operation, on the selective passage of gases and liquids through non-porous membrane elements by permeation or activated diffusion. Such passage is usually pictured as involving solution of gaseous or liquid material into one surface of a solid non-porous membrane element, migration of the material through the membrane element under the influence of a difference in concentration or pressure, and emergence of the material from another surface of the membrane element. Separation is obtained when different components of a fluid mixture pass through the non-porous membrane element at different rates. This type of separation involving differential permeation has been achieved, according to the known prior art, in membrane elements of platinum, palladium and their alloys; in membrane elements of silica and certain glasses; and also in membrane units of various polymeric materials.

The apparatus shown in FIGURES 1-4 comprises an elongat d flui ight tubular casing assembly 101 form of a suitable material such as steel. Tubular casing assembly 101 is preferable open at both ends. Both ends are provided with flange elements 102 and outwardly tapered portions 107. In addition the tubular casing assembly is provided with inlet and outlet means 108 and 109 to provide for movement of fluid into and out of the assembly. Preferably, means 108 and 109 communicate with the enlarged interior portion of the tubular assembly formed by tapered portions 107. A plurality of very small hollow filaments 111, of polymeric composition, such as polyethylene terephthalate for example, are positioned inside the tubular casing assembly 101 in a relatively close-packed relationship. As shown in FIG- URES l-4 the plurailty of filaments 111 comprises a number of substantially equal groups 110 of filaments each group firmly peripherally constrained by an elongated flexible porous sleeve member 112 extending longitudinally of the filaments and the groups. In addition, the groups 110 of filaments each surrounded by their porous sleeve members are all surrounded by at least one overall elongated flexible porous sleeve member 113 as shown. The detailed construction and functioning of these sleeve members will be discussed at a later point in this specification. Each end of the tubular casing assembly 101 is closed by a fluid-tight cast wall member 950 preferably formed of polymeric composition, such as an epoxy resin, for example. The hollow filaments, substantially parallel to each other and to the axis of the tubular casing assembly, extend between the cast wall members 950. The hollow filaments have open end portions which are embedded in and extend through the cast wall members in fluid-tight relation thereto. The tubular casing assembly 101 is further provided at each end with outer closure members 103 with cooperate with the tubular casing assembly 101 and the cast wall members 950 to define a closed chamber 130 in communication with the interior portions of the hollow filaments. Each chamber 130 is provided with conduit means 104 to permit movement of fluid between each chamber and a point outside the chamber. The outer closure members 103 are provided with flanges 105 which are secured to the flanges 102 of the tubular casing assembly by means of belts 106. In the preferred embodiment shown, an annular resilient gasket K of suitable material such as rubber or neoprene is provided between the cast wall members 950 and the tubular casing assembly 101 and between the cast wall members and outer closure members 103 to improve the fluid-tight sealing action. The outer closure members 103 are formed of a suitable material such as steel, for example.

As shown in FIGURE 2, the sleeve-encased groups of filaments 111 positioned in the main portion of the tubular casing assembly between the tapered portions 107 are relatively closely packed. The flexible constrainmg nature of the porous sleeve members 112 maintains the filaments in each group in a compact cross section while permitting each group to yieldably engage the other groups and the inside of the tubular casing assembly, in order to accommodate where necessary the cross sectional deformations necessary to achieve a packing condition of a higher degree than could be obtained by groups of rigid circular transverse cross sections. This is best shown in FIGURE 2a. The filament groups and the filaments themselves engage each other, and the casing assembly, laterally in a number of elongated areas or lines extending along the length of the groups and filaments (FIGURES 2, 2a, and 4). These elongated areas define between the groups, between the filaments, and between the groups and the interior of the casing assembly, a plurality of transversely evenly distributed elongated passageways extending along the length of the filaments and the tubular casing assembly. These passageways have very little lateral communication, and force circulation of fluid in the casing assembly and outside the hollow filaments to move, substantially longitudinally along the filaments and the interior portion of the tubular casing assembly between the tapered portions 107.

A positional relationship of the filament groups adjacent their ends and resulting from the tapered portion 107 of the tubular casing assembly, is shown in FIG- URE 3. It will be seen in this figure that the enlarged interior cross section at the tapered portion 107 reduces the packing density of the filament groups and increases the spacing between them to permit improved distribution and collection of fluid between the inlet and outlet means 108, 109 and the elongated passageways between the adjacent filaments, and groups of filaments.

The interior tapered end portion 107 of each end of the tubular casing assembly 101 cooperates with the corresponding tapered portion of the cast wall member 950 to develop a wedging action to help maintain the fluidtight seal between these parts. A similar action occurs as a result of the engagement between the engaged tapered portions of outer closure member 103 and the cast wall member 950.

An important feature of the apparatus involves the inner face SF of the cast wall members 950. This surface is relatively smooth, continuous, even, and substantially free of sharp deviations in the direction along which the hollow filaments extend. It is important that this configuration be achieved and maintained so that a fluidtight seal exists around the hollow filaments without diminishing the effective surface area of the filaments between the cast wall members. In a preferred embodiment of the invention, the inner surface SF of the cast wall members 950 has a concave curved configuration of a right circular cylinder, as shown. This configuration results from the centrifugal casting operation preferably employed to form the cast wall member 950 and which will be described in detail hereinafter.

The hollow filaments 111 may be composed of any polymeric material which is suitable for selective or differential permeation fluid separations. They may be made of olefin, ester, amide, silicone, ether, nitrile, or sulfide polymers; or of any other suitable polymer or copolymer. Suitable hollow filaments can be made from polyethylene terephthalate, polyvinyl chloride, polyvinylidene chloride, polyhexamethylene adipamide, copolymers of tetrafluoroethylene and hexafiuoropropylene, cellulose acetate, ethyl cellulose, polystyrene, copolymers of butadiene and styrene and many other polymers and copolymers. The filaments may be prepared in any suitable manner, such as by solution spinning or by melt spinning. The hollow polymeric filaments are preferably between about and about 500 microns in outside diameter and preferably have wall thicknesses between about 1 and about 100 microns. Hollow filaments between and 250 microns in outside diameter with wall thicknesses between 2 and 50 microns are especially preferred.

The density of packing of the hollow filaments 111 within the flexible porous sleeve members 112 may for practical purposes be of any convenient value above about but for optimum results should be as high as practicable. Packing density is defined as the percentage of the cross sectional area which is enclosed within the outer walls of the hollow filaments inside the tubular casing assembly 101. For a housing assembly of circular transverse cross section of inside diameter D containing N hollow filaments of circular cross section and outside diameter D the packing density is given as follows:

filaments parallel, surrounding them by a sleeve member, and reducing the peripheral dimension of the sleeve memher to compact the filaments contained therein. When groups of sleeve-encased compacted filaments have been bundled and drawn into tubular casing assemblies as shown in the drawings, packing densities of about 55% have been achieved. Overall packing densities above about 40% are preferred in the permeation units of the type sown in FIGURES l-4. These high packing densities do not prevent all movement of fluid into and out of the bundles between the filaments, but they do cause the fluids outside of the hollow filaments in the tubular casing assembly to flow along and in the direction of the filaments in a given group or bundle. This flow condition causes desirable concentration gradients to be established and maintained inside the housing assembly along the hollow filaments when a fluid mixture is passed through the hollow filaments in the housing assembly. This will be discussed in more detail at a subsequent point in the specification.

The flexible porous sleeve members 112, 113 may be made of any suitable material, natural, reconstituted, or synthetic, of suitable strength and compatible with the fluid mixture being handled, the polymer from which the hollow filaments are made, the material forming the cast wall members, and the other materials with which the sleeve will come in contact. The sleeve members may be of any practical construction which is porous and flexible.

Preferably the sleeve members should be of a strong abrasion resistant material, or a construction, which is capable of shrinkage or shortening at least in the transverse peripheral dimension to give a uniform constraining compacting action on and along an enclosed bundle or group of filaments. A preferred construction is a circularly knit fabric sleeve of a suitable material such as cotton thread, for example, which sleeve is capable of considerable reduction in transverse peripheral dimension when the sleeve is placed under tension longitudinally. This sleeve is especially advantageous, for when tension is exerted on such a sleeve surrounding a bundle to pull a filament bundle into a tubular casing assembly, the tension also results in uniformly compacting and reducing the bundle cross section along the bundle length to facilitate positioning the bundle in such a casing assembly without flattening or damaging the filaments of the bundle. The sleeve members 113 may also be made of woven, or non-woven fabric, or of punched or cut cylindrical tubes, or tubes of netting as shown in FIGURES 5a, 5b, 5c, and 5d. The ability of the sleeve member to shrink or reduce its radius or circumference uniformly and evenly is highly desirable and important.

The tubular casing assembly may be made with any suitable transverse cross sectional configuration and of any suitable compatible material of sufiicient strength. Cylindrical metallic housings, for example, steel pipe, are satisfactory, being reasonable easy to produce and assemble. The size of the tubular casings of the separation apparatus units may vary from less than one inch to many inches in outside diameter, and may vary from a few feet to many feet in length.

An idea of the effective construction and use of hollow filaments in the apparatus of this invention may be indicated by the fact that in a separation apparatus embodying features of this invention and having a tubular casing assembly about six inches in diameter and eight feet long, about twelve million hollow filaments have been packed to give an effective membrane surface area of about 20,000 square feet.

In certain forms of the fluid separation apparatus of this invention, it is desirable to introduce fluid adjacent each end of the tubular casing assembly (see final stage of FIGURE 8) and remove fluid from the assembly at a position intermediate its ends. Under these circumstances, it is desirable to provide an enlarged interior cross section for the assembly at this position intermediate its ends to reduce the packing of the filaments and filament groups for a limited distance to permit lateral flow and collection of fluid from between the filaments and filament groups.

The east end closure members 950 may be made of any convenient settable or solidifiable material of suflicient strength and compatibility with the other parts of the apparatus. Solders, cements, waxes, adhesives, natural and synthetic resins may be used. This cast wall member material may set or solidify because of freezing or cooling, or because of cooling, or because of chemical reactions which cause polymerization, condensation, oxidation, or other hardening processes. Other desirable properties of the settable or solidifiable material are: a low viscosity in the liquid form to promote easy penetration of filament bundles prior to solidification or setting, a high density to perform better under the centrifugal casting action (to be described in detail hereinafter), absence of gas evolution or similar physical change during solidification, minimum or no change in volume during solidification, and minimum evolution of heat during solidification. Synthetic organic resins are well suited for use as setting materials with the preferred polymeric compositions of the hollow filaments. The preferred materials from which the cast wall members are formed are epoxy resins.

In describing the operation and functioning of the apparatus unit shown in FIGURES 1-4, the description will first be given of the unit operating as first stage unit in a multi-stage system. In use as a first stage unit for the enumerated separations of gases (where the component filament walls to be separated from a fluid mixture represents only a small percentage of the mixture), it has been found advantageous to move the initial mixture through the interior of the hollow filaments and collect the permeated fluid from the outside of the hollow filaments. With respect to FIGURE 1, this general procedure is accomplished by bringing the inlet stream of the initial fluid mixture at elevated pressure into chamber 130 at the left hand end of the apparatus, as viewed in FIGURE 1, through conduit means 104. From this chamber 130, the fluid mixture then moves through the interior portions of the hollow filaments of filament groups 110 to a similar chamber 130 at the right hand end of the apparatus as seen in FIGURE 1. With a suitable pressure and/or concentration differential maintained between the inside and outside of the hollow filaments, a fraction of the initial fluid mixture enriched in the component with the highest permeation rate will permeate outwardly through the walls of the hollow filaments into the space between the inside of tubular casing assembly 101 and outside of the hollow filaments. The resulting fluid mixture, or efiluent, which reaches the chamber 130', somewhat depleted in the component with the highest permeation rate through the filament walls, is removed through conduit means 104.

The enriched fraction of the initial fluid mixture, or permeate product, which has permeated through the walls of the hollow filaments may then be removed from the interior of tubular casing at a lower pressure relative to that of the inlet stream, through a suitable outlet means such as 108. The preferred mode of operation involves the use of a sweep fluid stream, which may be a portion of the inlet stream at lower pressure, moved into the easing assembly 101 through inlet means 109, along the outside of the hollow filaments in the casing assembly, and out through outlet means 108. Sweep fluid flow in a direction countercurrent to the inlet stream flow is preferred in order to maintain desirable effective concentration gradients. Under these conditions, the close packing of the filaments and groups, which is made possible by the sleeve members 112, 113, together with the resulting longitudinally extending passageways between the filaments and groups, as discusesd previously, result in highly efficient evenly distributed fluid flow patterns inside casing assembly 101 and outside the hollow filaments in which flow patterns undesirable back mixing of the fluid outside the hollow filaments, and disturbance of the undesirable concentration gradients is kept to a low minimum. In addition, the large amount of effective membrane surface area present per unit volume of the casing assembly in its extremely small thickness, also contributes importantly to the efficient, practical, economically feasible fluid separation rates of this apparatus.

Under conditions in which the fluid mixture component to be separated (with the highest permeation rate through the hollow filament walls) represents a large percentage of the mixture, it has been found desirable to introduce the initial fluid mixture under elevated pressure into the interior of the tubular casing assembly 101 and outside of the hollow filaments through inlet means 109 and remove it as the effluent stream from outlet means 108 in condition depleted of its highest permeation rate component. In this mode of operation, a fraction of the initial fluid mixture enriched in the component with the highest permeation rate will permeate inwardly through the hollow filament walls into the interior of the hollow filaments from which it may be removed at lower pressure through conduit means 104 and/or 104' after being collected in chambers and 130. It is also desirable in this mode of operation to utilize a sweep fluid moving countercurrently to the flow of the initial fluid mixture, bringing it in through conduit means 104 and removing it and the permeate product through conduit means 104. This mode of operation has been found advantageous for the final stage apparatus units of a multistage gas separation system. However, it is understood that in other applications of the invention, such as water desalinization, or hydrocarbon separations other arrangements may be more advantageous.

Another desirable final stage version involves supplying the inlet fluid mixture into the casing assembly outside the hollow filaments at a point adjacent each end of the assembly and removing the depleted inlet mixture from the casing at a point between the ends of the casing (Final Stage FIGURE 6). In this version the fluid which permeates into the interior of the hollow filaments is removed simultaneously from both ends of the apparatus (Final Stage FIGURE 6), It will be noted that this establishes the desirable countercurrent flow of permeated fluid and inlet fluid mixture with its desirable concentration gradients.

With the preferred materials of construction, these apparatus units embodying principles of the invention can be operated satisfactorily at ordinary atmospheric temperatures and at moderate pressure levels, well below 1000 pounds per square inch for example, although the hollow filaments will easily sustain sufiiciently high pressure differentials to give commercially required flow rates. The flexible porous sleeve members 112, 113 which surround the groups of filaments not only serve a very useful purpose during assembly of the fluid separation apparatus of the invention but are important as a part of the apparatus combination itself in that they also continue to protect the hollow filaments during operation and function to maintain the lateral, or transverse, compressive stresses substantially evenly distributed throughout the entire bundle of closely packed hollow filaments Without flattening or damaging the hollow filaments, even those at the outer periphery of the bundle in contact with the tubular casing assembly walls.

The preferred use of centrifugally cast wall members to close the casing assembly ends and seal around the filaments is believed to be extremely important to the overall apparatus combination in achieving an effective uniform fluid-tight wall and seal between the very small closely packed filaments and between those filaments and the casing assembly, without wicking of the wall material (when in liquid form) between and along the filaments due to capillary action which could cause voids in the wall and would, by coating the filament surfaces, reduce the elfective membrane area within the casing assembly for permeation and separation.

The apparatus unit shown in FIGURES 1-4 can be combined in various forms and Ways to provide many different multi-unit and multi-stage separation systems if desired or required. A number of such systems are shown in FIGURE 6.

FIGURE 6 shows a preferred four stage separation system utilizing in each stage one or more separation units of the type shown in FIGURE 1 and made using the apparatus of this invention. The feed or inlet stream, entering the system through conduit 501 passes through a pressure regulating valve 502 and a control valve 504 actuated by an automatic controller 545 for final feed stream pressure control and then via conduit 505 into the interior of the hollow filaments of the first stage permeation unit 100. The depleted stream or effluent coming from the interior of the hollow filaments of the first stage permeation unit is conducted by conduit 506 to a control valve 507 actuated by an automatic controller 532 for eflluent pressure control. From valve 507 this stream passes through conduit 508 to vent, recycling, or other disposition. A portion of the feed stream is diverted through a flow sensing device 534, conduit 533, pressure regulating valve 541, conduit 539, control valve 538, and conduit 540 into the casing assembly of the first stage permeation or separation unit 100 as a sweep stream, This sweep stream and the fluid permeated outwardly through the hollow filaments of the first stage permeation unit is carried from the casing assembly of the unit by conduit 509 to compressor unit C1 and thence via conduit 510 into the interior of the hollow filaments of the second stage permeation unit 100. The depleted stream or effluent coming from the interior of the hollow filaments of the second stage separation, or permeation, unit is carried via conduit 511, control valve 557, and conduit 591 as a recycle stream to join with the inlet stream supplied by conduit 505 to the interior of the. hollow filaments of the first stage separation unit. The fluid permeated outwardly through the hollow filaments of the second stage separation unit is carried out of the casing assembly of this unit by conduit 513 to compressor unit C2. From compressor unit C2 this stream is supplied as an inlet stream via conduit 514 into the casing assembly of the third stage separation unit 100 at two spaced inlet points each adjacent one end of this casing assembly. The depleted stream or efiiuent from the casing assembly of the third stage separation unit is removed therefrom at a point on the casing assembly between the two inlet points by conduit 515 and passes through pressure regulating valve 516, and conduit 517 to be recycled into the inlet stream to the second stage separation unit carried by conduit 509. The stream of fluid which permeates inwardly through the hollow filaments of the third stage separation unit is removed from both ends of the interior of the hollow filaments and the unit by means of conduits 518, 519 and carried via conduit 520 to compressor C3. From compressor unit C3 this stream is supplied as an inlet stream via conduit 521 into the casing assembly of the fourth and final stage separation unit at two spaced inlet points each adjacent one end of the casing assembly. The depleted or effluent stream from the casing assembly of the fourth stage separation unit is removed therefrom at a point on the casing assembly intermediate the two inlet points and moves for recycling through conduit 522, pressure regulating valve 523, and conduit 524 to be recycled into the inlet stream to the third stage separation unit carried by conduit 513. The stream of fluid which permeates inwardly through the hollow filaments of the fourth stage separation unit is the final permeate product and is removed from both ends of the interior of the hollow filaments and the unit by means of conduits 525, 526

and carried to storage or use by conduit 527. The composition, or concentrations of the permeate product 10 stream is preferably continuously monitored by analyzer unit 578,

Each compressor unit is provided with a by-pass vacuum breaker arrangement as shown to control the pressure of the permeate streams.

The flow rates of the effluent streams from the third and fourth stage separation units were controlled by control valves 566 and 575, in conduits 567 and 576 respectively, to maintain the desired concentration or compositions of these streams and of the final permeate product.

The system is provided with process control unit 551 which alternately analyzes the effluent stream concentration or composition leaving the first stage separation unit and the recycled stream concentration or composition leaving the second stage separation unit. A bleed line or conduit 560, having a pressure regulating valve 561 therein connects the efi luent stream in conduit 506 to unit 551 for analysis and a bleed line 562 having pressure regulating valve 563 therein connects the recycle stream in conduit 511 to unit 551 for analysis. A signal representative of the analysis of effluent (concentration or composition) in conduit 506 is transmitted via conduit 550 to controller unit 547 which compares the signal with the desired or set-point concentration or composition and generates an error or difference signal which is transmitted to controller unit 536. A rate of flow signal generated by flow sensing device 534 is transmitted to controller unit 536. With these two inputs, controller unit 536 actuates control valve 538 to maintain a desired predetermined concentration or composition in the effluent stream from the first stage separation unit. A signal representative of the analysis of recycle concentration or composition in conduit 511 is transmitted via conduit 552 to controller unit 553 which compares the signal with the desired or set-point concentration or composition and generates an error or difference signal which is transmitted to controller 555. A pressure difference signal generated by pressure sensing device 559 connected across conduits 511 and 510 is transmitted to controller 555. With these two inputs, controller unit 555 actuates control valve 557 to control the flow in conduit 511 and maintain a desired predetermined concentration or composition in the recycled effluent stream from the second stage separation unit.

Summarizing generally the operation of the FIGURE 6 system, the flow of sweep fluid to the casing assembly of the first stage separation unit is adjusted by means of control valve 538 and controller units 547 and 536 to maintain a predetermined low concentration, or composition, of the more permeable components in the depleted effluent carried by conduit 506. In addition, the flow of either the second stage recycle stream, the third stage recycle stream, or the fourth stage recycle stream is adjusted in response to changes in the concentration, or composition, of the second stage permeate stream, the third stage permeate stream, or the fourth stage permeate product stream, The preferred arrangement as illustrated in FIGURE 6 is to control the rate of the second stage unit recycle stream to maintain a desired high concentration of the more permeable component in the fourth stage permeate product stream. Such a system with this process of operation is especially useful in recovering a high fraction of a high purity product from a fluid mixture containing a low concentration of a more permeable component, as for example in recovering helium from natural gas.

A pilot plant for recovering helium from natural gas using a four stage system embodying principles of this invention and of the type shown in FIGURE 6 was built and operated successfully. The system utilized hol low filament membrances of poly(ethylene terephthalate) with outside diameters of about 29.2 microns and inside diameters of about 15.5 microns. The first stage arrangement contained a number of separation units connected in parallel with a total of about 50 million hollow filaments with effective lengths of about 200 cm. and an effective total area of about 73,000 square feet. The second stage arrangement contained about 11 million hollow filaments with effective lengths of 75 cm. and an effective total area of about 617 square feet. The first and second stage arrangements operated with the feed or inlet streams supplied into the interior of the hollow filaments. The third and fourth stage arrangements operated with the feed or inlet streams supplied into the casing assemblies outside of the hollow filaments, each having active filament lengths of 86 cm., with about 10,400, and 3200 hollow filaments respectively and effective areas of about 66.4 and about 20.3 square feet respectively. This system included automatic control units for adjusting the flow of sweep gas to the first stage arrangement in response to analysis of the depleted effluent gas from the first stage arrangement, and for adjusting the flow of the secoond stage recycle stream in response to analysis of this recycle stream. In addition, the desired concentration of the recycle stream was changed or controlled in response to changes in the helium content of the fourth stage final permeate product. This pilot plant system operated continuously with minor fluctuations in flow rates and gas mixture compositions under the following conditions (minor losses and those due to sample streams are not indicated) (Table I):

TABLE I Flow Helium Stream in percent by conduit No. Stream description Pressure (s.c.f.m.) volume) System feed 740 p.s.i.g. 51. 0. 50 503 do l 315 p.s.i.g 50.9 0.50 1st stage sweep 22.5 in. Hg- 0.12 0. 50 1st stage feed 315 p.s.i.g- 51. 6 0. 59 1st stage effluent- 248 p.s.i.g 49. 7 0. 032 1st stage permeate -22.5 in. Hg 2. 13.1 2nd stage feed". 375 p.s.i.g 0.91 13.0 2nd stage recy0le 345 p.s.i.g 0.76 3. 8 2nd stage permea 15. 5 in. Hg 0. 15 59. 8 3rd stage feed 200 p.s.i.g 0. 61 515- 3rd stage receyle 200 p.s.i.g 0.06 10 518, 510 3rd stage permeate 0 p.s.i.g 0. 04 85 5'21 4th stage feed 110 p S g- 0. 025 85 522 4th stage recycle 0.016 74 525, 526 4th stage penneate O. 010 99. 9

(product).

A preferred arrangement embodying principles of the invention for manufacturing the improved fluid separation apparatus described is illustrated in FIGURES 7-17 of the drawings.

Continuous hollow filaments either in the form of monofilament or multi-filament yarns are received in wound packages P which are positioned as shown on a supply frame structure 700 (FIGURE 7) which comprises vertical members 701 interconnected with horizontal members 702 preferably supported on wheels or rollers W. The filaments 111 or yarns from each package are led through suitable guide elements E carried by the supply frame structure to a suitable rotary apparatus 800 which winds up the hollow filaments to simultaneously form a plurality of skeins or hanks 110 as shown in FIGURE 7. The rotary apparatus shown comprises a base 703, a vertical support 704, in which is journalled a horizontal shaft 705. Shaft 705 is provided at one end with a pulley wheel 706 which is driven by an endless belt or chain 707. Shaft 705 carries at its other end a circular member 708 which carries a plurality of radially extending elements 709 each carrying a laterally extending hank supporting element 710. Each element 710 is provided with cut out portions 711 for receiving the hanks 110 formed by winding up the hollow filaments from the package P.

After hanks 110 of suitable size are formed, rotation of apparatus 800 is terminated and the hanks removed therefrom. Each hank is then engaged at two diametrically opposed positions by suitable means such as hook elements 720 andby manipulating the hook elements as shown in FIGURE 8 the hank is flattened and elongated as shown to form a single compact bundle. While each bundle is maintained in this configuration by sufiicient tension applied to the hank elements 720, a porous flexible sleeve 112, preferably of a circularly knit construction as described in the preceding portions of the specification, is placed around the bundle and extending longitudinally along the bundle. As previously described the porous sleeve member 112 is of a construction such that tension applied to it longitudinally causes its transverse dimension, or periphery to diminish. The sleeve member 112 may be applied by placing it in accordian like pleated or folded configuration on a smooth annular bushing or guide N as shown in FIGURE 9. Then, with the bushing and sleeve member surrounding one end of the filament bundle 110, the bushing is moved toward the other end of the bundle and the sleeve member allowed to pull off the bushing and engage the filament bundle in a snug constraining fit uniformly along the bundle length as indicated in FIGURE 9. It will be seen that longitudinal tension applied to the ends of the sleeve member will cause the reduction in the sleeve member transverse periphery to compact and compress the hollow filaments into a closely packed bundle or hank. As discussed previously, the flexible porous sleeve member is formed of a sufficiently strong and abrasionresistant material and construction not only to maintain the compacting compressing action but also to protect the filaments during assembly and operation of the apparatus.

A plurality of sleeve-encased filament bundles or groups prepared in accordance with the preceding description are assembled and suspended at one end in a parallel vertically extending relationship as shown in FIGURE 10 by means of an annular ring or a plate element 721 to which are hooked or secured the hook elements 720 which carry the sleeve-encased filament groups or bundles. The plate element 721 is supported by suitable means such as the vertical chain 723 which, as shown in FIGURE 11, is led through the interior of a tubular casing assembly 101. The thus suspended plurality of sleeve-encased filament bundle or group is then further encased, as shown in FIGURES 11 and 12, by one or more larger flexible porous sleeve members 113 in a similar manner to that shown in FIGURE 9 for encasing the individual groups. The one or more larger sleeve members are then tensioned longitudinally to compact the plurality of groups into one compact cross section composite bundle which is of a size which can be drawn into the interior of the casing assembly 101 by tension or chain 723. The lateral or transverse compacting action of the sleeve members is sufficient to enable positioning of a closely packed bundle in a casing assembly to substantially fill the interior of the casing assembly with tightly packed filaments without flattening or damaging any of the hollow filaments which are in the small sizes used very fragile and susceptible to damage in handling. It is believed that it would be impossible to compress the same number of hollow filaments in a single large bundle suificiently to give a close packing arrangement in a casing assembly by merely compressing the bundle from its outer periphery, without fllattening or damaging at least those filaments around the outer periphery of the bundle. Other desirable aspects of assembling filament groups in the porous sleeve members and alternate sleeve member constructions have been discussed earlier in this specification.

When the single large composite sleeve encased bundle of hollow filaments has been positioned in the tubular casing assembly 101, a mold unit 905b is bolted to the end of the casing assembly 101 as shown in FIGURE 13, previous to which, if desired, an annular resilient gasket member K of suitable material, such as rubber or neoprene, is positioned in the tapered end portion of the easing assembly as shown in FIGURE 13. The mold unit 905b, in operative position, is secured in fluid tight relationship to the flange 102 of the casing assembly 101 by suit able means such as mold flange 907 and bolts 906. The

mold unit is provided with a mold cavity MC which, in operative position, surrounds the ends of the groups of filaments making up the end of the large bundle of filaments as shown in FIGURE 13. The mold unit 905b is also provided with an inlet means 908a communicating with the the mold cavity MC for the supply of the liquid molding material.

During rotation of the casing assembly 101 with the attached mold unit 905b so that centrifugal force acts in the direction of arrow CF in FIGURE 16, a solidifiable liquid, such as an epoxy resin mixture or other material as described in preceding portions of the specification, is introduced into the mold cavity surrounding the end of the filament bundle and engaging the interior tapered portion of the casing assembly. The centrifugal force developed by the rotation is sufficient to keep the solidifiable liquid from wicking along the hollow filaments into the interior of the casing assembly and maintains the liquid in a configuration with an inner surface SF which is relatively smooth, continuous, even and substantially free of sharp deviations in the direction along which the filaments extend. The liquid surface SF is also maintained by the rotation and centrifugal force in a concave cylindrical shape as shown in FIGURES l and 13. While continuing this rotation, the liquid is caused to solidify to form the fluid tight cast wall member 950 surrounding the filaments and engaging the casing assembly. The cast wall member with the mold unit removed is shown in FIGURE 14. The next step required is the severing of the end of the cast wall member and the looped ends of the filaments of the bundle by severing or cutting the cast wall member along line CL shown in FIGURE 14. This opens the ends of the hollow filaments embedded in and extending through the remaining portion of the cast wall member. One satisfactory method of accomplishing the severing action involves initially sawing through the cast wall member 950 followed by a shaving operation with a razor-sharp instrument to open or clear the hollow filament ends. Assembly of this end of the apparatus is completed by securing an outer end closure member 103 to the casing assembly as shown in FIGURE 1. The same technique may be used to complete the other end of the apparatus unit.

In an alternate casting technique for forming the cast wall member, the same procedure is followed except that an immiscible liquid more dense that the solidifiable material forming the wall member, is also supplied to the mold cavity during rotation. Naturally under the centrifugal action, this more dense liquid is positioned between the solidifiable liquid and the outer wall of the mold cavity and is controlled so that upon solidification of the casting liquid and removal of the more dense material, a cast wall member is formed as shown in FIGURE 15 in which the looped end portions of the filament bundle are exposed. In order to complete the formation of this cast wall member, it is only necessary to cut off the end portions of the filament bundle along line CL shown in FIGURE 15 and open the end portions of the hollow filaments embedded in and extending through the cast wall member. It is desirable to first add the solidifiable material to the mold cavity and then add the immiscible more dense liquid. This results in a coating of the end portion of the hollow filaments by the solidifiable material which coating persists through the application of the immiscible liquid and solidifies in a thin coating on the filament end portions which makes them much easier to cut.

A number of suitable materials can be used as the immiscible liquid provided it is more dense than the setting, or solidifiable material, unreactive with the hollow filaments, and solidifiable material, and can be removed. The material may be hardenable temporarily by gelatin, polymerization or otherwise if it can be conveniently removed by heating, depolymerization, or dissolution without affecting the solidified cast wall member. Water is a convenient immiscible liquid for use with some solidifiable materials and if desired may be thickened or gellied with agar, gelatin, polyvinyl alcohol or the synthetic or natural gums. Low melting point paraffin waxes and hydrocarbon oils thickened into greases may also be used. However, the preferred immiscible liquid for use with epoxy resin setting materials are halogenated fluids such as the Kel-F fluorocarbon oils sold by the Minnesota Mining and Manufacturing Company. These oils are sufliciently more dense than epoxy resins and form a sharp interface therewith under moderate centrifugal forces.

FIGURES 16 and 17 show a preferred and an alternate apparatus for forming the cast wall members of the separation units of the invention.

FIGURE 16 shows a permeation separation unit like that of FIGURE 1 suitably mounted on a preferred cen trifugal apparatus ready for casting of the cast wall mem bers 950. Removable mold units 9050 and 905b are fastened in a fluid tight manner to flanges 102 and casing assembly 101 by means of bolts 906 and flange 907. Inlet fittings 908a and 90812 through which the solidifiable wall material flows into the molds 905a and 905b are shown near the extreme ends of the mold units but may be at other locations as desired.

The centrifugal apparatus shown includes a stationary tubular housing or other suitable support 909, a rotating shaft (not shown), a drive pulley 911, a belt 912, a motor 913, a pedestal 914, a base 915, a clamping assembly 916, and other parts as required for support and rotation.

Suitable means for feeding a setting or solidifiable liquid to the molds 905a and 90512 are also mounted on or part of the centrifugal apparatus. This means may be the hydraulic slip ring assembly 917 of FIGURE 16. This slip ring assembly includes a block of suitable material mounted on the centrifugal apparatus which contains in its upper surface grooves 918a etc. in to which the setting or solidifiable liquid can be introduced and from which the setting liquid can flow to molds 905a and 90512 through tubes 919a etc.

The hydraulic slip ring 917 may contain two, four, or more grooves 918a etc. to allow for feeding casting liquids at one or more levels into molds 905a and 9051:. These grooves 918a etc. are conveniently slightly eccentric toward their outlets to induce the casting liquid to flow under centrifugal force toward their outlets and through tubes 919a etc. toward the molds. The grooves 918a etc. are also conveniently shaped to prevent flow of the casting material over their outside edges during rotation.

Casting liquids may be introduced into the hydraulic slip ring assembly 917 in any convenient way. For example, they may be retained in containers 920a etc. and metered through valves 921a etc. through tubes 922a etc. leading to grooves 918a etc. This hydraulic slip ring and its associated parts provide for convenient and effective introduction of casting materials into molds 905a and 9051) while the centrifugal apparatus is in operation.

Before casting a wall member with the centrifugal apparatus of FIGURE 16, the following preliminary operations are completed: Hollow filaments are assembled and installed within casing assembly 101. Mold units 905a and 905k are then fastened to the ends of the casing assembly as shown. Final adjustment and trimming of the center of gravity of the complete assembly may be attaching ordinary threaded nuts to the ends of tie bolts 906. After the unit is statistically balanced, it is mounted on the centrifugal apparatus and clamped in place by suitable means. Hydraulic slip ring 917 is then assembled in place and feed lines 919a etc. are connected to the various fittings on mold units 905a etc. into the appropriate outlets of hydraulic slip rings 917.

The centrifugal casting operation then includes the following steps: Motor 913 is energized and the centrifuge is brought up to a speed which subjects mold units 905a etc. to the desired centrifugal force. A setting or solidifiable liquid (and immiscible liquid, if used) is then introduced into the mold cups through the hydraulic slip ring and its various parts. The setting material is introduced at a convenient rate which allows sufficient time for the material to penetrate and fully impregnate the interstices of the hollow filaments in the mold cavity uniformly. After the liquid has reached the desired level, further addition is stopped. During the addition of the setting liquid the centrifuge is operated, as previously mentioned, at a speed which subjects the material within the mold units to the desired centrifugal force. Rotation is continued for a sufficient time to permit solidification of the setting liquid until it will maintain its shape.

When the setting material has sufiiciently hardened, rotation is stopped and the separation unit is removed from the centrifugal apparatus. The unit may be set aside to allow further hardening of the setting material if desired. The final fabrication steps involve draining of the immiscible liquid, if used, removal of the mold units, cutting or otherwise breaking the hollow filament end portions (and the setting material if no immiscible liquid was used) to open the ends of the hollow filaments to fluid flow, and adding the outer end closure members 103 to form the head spaces 130, 130 of the separation unit. The unit is then ready for operation when provided with other necessary fittings and suitably connected to a source of the mixture to be separated and to means for removing the separated products.

FIGURE 17 shows another alternate type of centrifugal apparatus for casting cast wall members 950 in separation unit casing assemblies. This centrifugal apparatus includes a stationary support housing 923, spindle 924, motor 925, and other mechanical parts as necessary for support and rotation. A hydraulic slip ring assembly 917 may be mounted on spindle 924 with flexible tubes 919a etc. connecting slip ring 917 with molds 905a etc. At the upper end of spindle 924 is mounted platform 929 to which are rigidly attached trunnions 926a etc. These trunnions are equally spaced around the platform and diametrically opposed. Two, four, or more tubular casings 101 are pivotally attached to trunions 926a etc. by means of clevices 927a etc., one end of each clevis being attached to a flange 102 of a casing assembly 101, while the other is journalled to a trunion 927 with a pin 928. As shown by the dotted lines in FIGURE 17, tubular casings 101 hang vertically when the centrifuge is not operating. The method of operation of this apparatus is generally the same as that followed in the operation of the FIGURE 16 centrifugal apparatus.

The position of the openings 908a (FIGURE 13) through which the setting liquid is passed into the mold units can be varied as convenient. These openings may be located in the bottoms of the molds, so the setting material or immiscible liquid will progressively displace air from the extremities of the hollow filament bundles toward the center of the bundles, or the openings may be on the sides of the molds. The bottom location will usually be preferred when using an immiscible liquid and when using a setting material which tends to wick unevenly in the assembled hollow filaments, but the side location will be preferred when it is desired to add the setting material on top of an immiscible liquid, when the setting material tends to shrink on setting, and when it is desired to feed additional liquid setting material on top of partially set material to insure complete filling of cracks and voids resulting from shrinkage. Also, several openings can be provided at different locations on any particular mold cup, each with an associated feed system, so that the immiscible liquid and part of the setting material can be fed at one location and other parts of the setting material can be fed at one or more different locations.

When using an immiscible liquid, the liquid may be introduced into the mold either before or after the setting material. Addition of the liquid before the setting material may be preferred when it can be conveniently added through openings at the bottom of the mold and the setting material can be added through openings at the top of the mold. Addition of the setting material before the more dense immiscible liquid is preferred when both are to be added through openings at the bottom of the molds. Addition of the setting material first is desirable when the immiscible liquid wets the hollow filaments and is not easily displaced from their surfaces by the setting material. Addition of the setting material first is especially desirable when the setting material wets the hollow filaments and is not completely displaced by the immiscible liquid. Under these conditions, a thin film of the setting material hardens on the follow filaments and stiilens them to simplify and make more efiicient the later step of cutting them to open their bores for flow. Addition of the setting material first is also desirable when the immiscible liquid wets the hollow filaments because it makes practical the production of strong seals in which the hollow filaments are distributed uniformly throughout the potting area. Addition of the immiscible liquid first requires that the hollow filaments be relatively separate and far apart so the setting material will flow between the hollow filaments to form a uniform seal rather than remain near the inlet and force the immiscible liquid into areas which the setting material is intended to occupy.

The magnitude of the centrifugal force required to obtain the advantages of this invention depends on many factors. Important is the size and packing density of the hollow filaments, the viscosity and other flow properties of the setting material, the surface tension forces between the setting material and the hollow filaments and between the setting material and the walls of the mold unit,

the relative densities of the hollow filaments and the setting material, and (in the alternate form of centrifugal apparatus in which the supports and the molds swing in response to centrifugal force) the weight and shape of the supports and molds.

In practice, centrifugal forces between a few times the force of gravity and several hundred times the force of gravity may be effective. The preferred range of centrifugal forces is between about 50 times gravity and about 200 times gravity. The minimum effective force may be between 5 and 25 times the force of gravity. Forces above about 900 times gravity however may be so great as to collapse the walls of thin-walled hollow filaments of polymeric materials and should be avoided. The centrifugal force used is easily controlled by varying the speed of rotation of the centrifuge as indicated by wellknown mathematical expressions.

It is believed to be apparent that in accordance with the objects of the invention novel and improved production apparatus has been provided for use in manufacturing the specialized and novel gas separation units described.

Although a number of preferred embodiments have been described in detail in accordance with the Patent Statute, many modifications and variations Within the spirit of the invention will occur to those skilled in the art, and all such are considered to fall within the scope of the following claims.

What is claimed is:

1. For use in the manufacture of fluid separation apparatus of the type comprising an elongated tubular casing assembly, said casing assembly comprising a first end, said end being closed by a cast wall member of polymeric composition, a plurality of very small diameter filaments of polymeric composition and having hollow interior portions, said filaments extending from said cast wall member through said casing assembly and having open end portions extending through said cast wall member; a centrifugal casting apparatus for forming a cast wall member extending transversely across an elongated bundle of substantially parallel hollow filaments, said apparatus comprising, a supporting base structure, a rotatable assembly mounted on said base structure for rotation about a given axis, drive means cooperating with said rotatable assembly to rotate the same about said axis, means mounted on said rotatable assembly for supporting an elongated bundle of substantially parallel hollow filaments and securing said bundle for rotation with said assembly, said bundle having two end portions, in a position in which said given axis is substantially perpendicular to the direction in which said filaments and said bundle extend, said axis being spaced from the end portions of said bundle, said apparatus further comprising a mold unit carried by said rotatable assembly and having a mold cavity formed therein, said mold unit and its cavity constructed, arranged, and positioned to surround and contain one end portion of a bundle of filaments supported and secured on said rotatable assembly, and to maintain a mass of liquid in engagement with the said one end portion of such a bundle during rotation, and means carried by said rotatable assembly and cooperating With said mold unit for introducing a solidifiable liquid into engagement with the said one end portion in said mold cavity during rotation of said assembly, said mold unit and said bundle, said drive means arranged and operated to rotate said rotatable assembly, hollow filament bundles and mold units carried thereby at speeds such that the centrifugal force developed maintains said solidifiable liquid in desired position during its solidification in said mold cavity during rotation and in a bubble-free void-free condition and in addition said centrifugal force prevents wicking or movement of said liquid along and between said filaments of said bundle due to capillary action by opposing the forces of such capillary action.

2. For use in the manufacture of fluid separation apparatus of the type comprising an elongated tubular casing assembly, said casing assembly comprising a first end, said end being closed by a fluid-tight centrifugally cast wall member of polymeric composition, a plurality of very small diameter filaments of polymeric composition and having hollow interior portions, said filaments maintained substantially parallel and in a compact bundle by a flexible porous sleeve member extending along said bundle, said filaments extending from said cast wall member through said casing assembly and having open end portions extending through said cast wall member; a centrifugal casting apparatus for forming in place a cast wall member extending transversely across an elongated bundle of substantially parallel hollow filaments and across the casing assembly, said bundle formed of a hank of continuous hollow filaments and having end portions each comprising a plurality of loops of said continuous filaments as they traverse the bundle, said apparatus comprising, a supporting base structure, a rotatable assembly mounted on said base structure for rotation about a given axis, drive means cooperating with said rotatable assembly to rotate the same about said axis, means mounted on said rotatable assembly for supporting a tubular casing assembly containing a sleeve encased elongated bundle of substantially parallel hollow filaments and securing said casing assembly for rotation with said rotatable assembly, said casing assembly and contained bundle having two end portions, in a position in which said given axis is substantially perpendicular to the direction in which said filaments and said bundle extend, said axis being spaced from the end portions of said bundle, said apparatus further comprising a mold unit carried by said rotatable assembly and having a mold cavity formed therein, said mold unit and its cavity constructed, arranged, and positioned to cooperate with said ends of said tubular casing assembly positioned and secured on said rotatable assembly and surround and contain one end portion of a bundle of filaments in said casing assembly, and to maintain a mass of liquid in engagement with the said one end portion of such a bundle during rotation, and means carried by said rotatable assembly and cooperating with said mold unit for introducing a solidifiable liquid into engagement with the said one end portion in said mold cavity during rotation of said assembly, said mold unit and said bundle, said drive means operated to rotate said rotatable assembly, casing assembly, hollow filament bundles and mold units carried thereby at speeds such that the centrifugal force developed maintains said solidifiable liquid in desired position during its solidification in said mold cavity during rotation and in a bubble-free void-free condition and in addition said centrifugal force prevents wicking of said liquid along and between said filaments of said bundle due to capillary action by opposing the forces of such capillary action.

References Cited UNITED STATES PATENTS 1,317,120 9/1919 Wolever.

2,550,858 1/1951 Parrett.

2,597,934 5/1952 Kennison.

2,633,605 4/ 1953 Brucker.

2,686,951 8/1954 Seaman.

3,046,631 7/ 1962 Olivier.

3,297,802 1/1967 Powers.

3,382,541 5/1968 Campbell.

WILLIAM J. STEPHENSON, Primary Examiner US. Cl. X.R.

mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,99 9 Dated February 3, 97

Inventor(s) Geary, Harsch, Maxwell and Rego It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 38, the Patent No. should read 3,ML2,002 same column, line 39 should read issued May 6, 1969 to Geary et a1.

SIGNED A D SEALED ms 181% (SEAL) Am 'W' mm x. 501mm. .18. Attesfing Offic r oomissionar or Patents 

